Arctic glider yields unrivaled under-ice data

U. WASHINGTON (US)—A seaglider’s record-breaking journey under ice is helping scientists form a more complete picture of changes taking place in Arctic waters.

A University of Washington (UW) team recently set a world record by successfully operating one of its seagliders for six months as it made round trips hundreds of miles under the ice at Davis Strait. The result contributes to the longest continuous measurement of fresh water exiting the Arctic through the Canadian Arctic Archipelago and Davis Strait and into the Labrador Sea.

There are concerns that climate change may increase the amount of fresh water so much that it impacts the formation of very dense water in the Labrador Sea. That dense, cold water is a critical component driving the circulation of the world’s oceans, according to Craig Lee, a principal oceanographer with the University of Washington’s Applied Physics Laboratory. Lee and senior oceanographer Jason Gobat lead the group developing the under-ice seaglider.

The project is one of more than 35 included in the National Science Foundation’s Arctic Observing Network, an effort designed to track and understand Arctic environmental change using tools ranging from ocean buoys to satellites.

UW’s seagliders are small, reusable underwater vehicles meant to operate on their own, gliding without propellers from the surface to as deep as 1,000 meters, or 3,300 feet, while collecting such information as temperature, salinity and level of dissolved oxygen. When seagliders are at the ocean surface they can be commanded remotely from nearly anywhere in the world via the Internet and can transmit their data via satellite telephone. Unlike faster-moving propeller-driven autonomous underwater vehicles, which may need to be retrieved by ships only days after being deployed, UW seagliders can operate on their own for months at a time.

The ability to do so under ice is important in a place such as Davis Strait where scientists want to measure how much fresh water flows through the strait and at what times of year so they have a baseline for comparison in coming years.

Early development of the seagliders was paid for by the Office of Naval Research. The National Science Foundation funded work to add under-ice capabilities so it might take samples in harsh Arctic waters.

“This cutting-edge technology has the potential to make year-round measurements over broad areas where access by other means is severely limited, due to the presence of sea ice for part or all of the year,” says Martin Jeffries, Arctic Observing Network program director.

Moorings—strings of instruments tethered to the seafloor—also are monitoring water in Davis Strait but are not ideal for detecting plumes of fresh water, Lee says. The freshest water is often found in a thin layer about 50 meters thick, or 165 feet, just under the sea ice. Tethering an instrument atop a mooring so it reaches that thin layer puts the instrument at risk of being ruined if an especially thick, low-hanging piece of ice comes along and strikes it.

According to Lee, seagliders pass through that upper layer as they dive from the top to the bottom of the strait and so can supply data in places that instruments on the mooring cannot.

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